This invention relates to a latex composition. More particularly, this invention relates to a latex composition comprising a polymeric latex and an extender.
The term "latex" was originally applied to aqueous dispersions of natural rubber. This term is now used in the art to refer to aqueous dispersions of natural rubber, aqueous dispersions of synthetic elastomers and mixtures thereof.
Latex has a wide variety of commercial uses. The latex composition of the present invention is particularly suitable for laminating textiles, i.e., carpeting. In the manufacture of carpeting, particularly tufted carpeting, it is the general practice to coat the back of the carpet with a latex composition. In the case of tufted carpeting, this coating acts as an adhesive to secure the tufts in place so that they are not pulled out in normal use. A secondary backing or layer is sometimes applied to carpeting. Materials used for this purpose are woven jute, scrim or a woven or non-woven textile made of such synthetic materials as polypropylene, rayon, viscose, nylon, polyester acrylics or mixtures thereof. The principal purpose of this secondary backing or layer is to provide additional dimensional stability and stiffness to the carpet. A foamed material, such as a filled latex mixture which is foamed by beating in air, may also be applied as a secondary layer. Generally, after the foamed material is applied it must be dried and cured by the application of heat. This backing also increases the dimensional stability of the carpet and imparts a springiness when it is walked upon. However, the foamed type of secondary layer does not provide the stiffness that is generally provided by the secondary layer composed of the aforementioned materials. The secondary layers mentioned above are generally laminated to the carpet by the use of a latex composition.
Our U.S. Pat. No. 3,779,857, which is incorporated by reference in this case, discloses the use of a ternary mixture of granular starch, urea and borax as an extender for latex laminating compounds. Although this ternary mixture has been found to be exceedingly effective as an extender, the drying rate of the laminating material containing the ternary mixture is not as rapid as is sometimes desired.
We have now discovered that an extender consisting essentially of granular starch and borax in certain proportions and amounts can be used in polymeric latexes without substantially deleteriously affecting the functional properties of the latex while providing increased drying rates. Broadly, the weight ratio of granular starch to borax is from about 15:1 to about 12:1 and preferably is from about 10:2 to about 9:2. Up to about 66 parts by weight (basis 100 parts of latex polymer solids) of the extender consisting essentially of granular starch and borax may be used, although it is preferred that the latex composition contain up to about 25 parts by weight of extender when the composition is to be used for laminating textiles.
In the following discussion and in the Examples, the abbreviation "pbw" refers to parts by weight and is based upon the 100 parts of the latex polymer solids present unless otherwise specifically noted.
The latex composition of the present invention may contain materials which are generally used in latex compositions. For instance, since the present composition is particularly suitable for laminating carpeting, it may contain relatively large amounts of inorganic fillers. Exemplary of inorganic fillers are bentonite, CaCO.sub.3, clays, colloidal silicates, diatomaceous earth, hydrated alumina, and zinc oxide. These fillers, in some cases, provide beneficial secondary properties to the composition such as opacity, fire retardance, stiffness and color. Generally, these fillers may be used in amounts up to 875 pbw, although it is preferred to use amounts up to 500 pbw in the composition of the present invention.
A wide variety of polymeric latexes may be used in the present composition. In the case of the composition being used for laminating textiles, it is preferred that the polymeric latex be cold SBR latex, cis-polyisoprene latex, butadiene, natural rubber latex, carboxylated butadiene-styrene latex, ethylene vinyl acetate latex, ethylene vinyl chloride latex or various mixtures thereof. These latexes require, if any, only small amounts of curing agents but must, however, be cured by the application of heat. The temperature at which the latex is cured must be below the thermal degradation temperature of the textile to which it is applied and thus, in most cases, must be below 300.degree. F. Generally, latexes in which the polymer chain contains various functional groups pendant therefrom exhibit low temperature curing properties. Such polymers are made by the emulsion interpolymerization of a conjugated diene, such as butadiene, with an ethylenically unsaturated functional monomer, for instance, .alpha., beta-, unsaturated carboxylic acids, mono-esters of such dicarboxylic acids, acrylamides, N-methylol acrylamides, and the like. In addition to the functional monomer, there may also be present in the present composition one or more secondary copolymerizable monomers such as styrene, acrylonitrile, methyl methacrylate, vinylidene chloride, vinyl toluene, .alpha.-methyl styrene and the like.
The presence of the secondary copolymerizable monomers is principally responsible for the stiffness and flexibility characteristics imparted to the laminated textile, the greater the proportion of secondary monomers, the less flexible and the stiffer is the laminated textile. In this respect, to obtain these characteristics to an optimum degree it is preferred that the amount of conjugated diene be from about 40 to about 75 pbw and the amount of secondary monomer be from about 60 to about 25 pbw. The most preferred composition contains amounts of conjugated diene of from about 45 to about 70 pbw and amounts of secondary monomer of from about 55 to about 30 pbw.
Copolymerized latexes may be prepared by methods well known in the art, such as emulsion polymerization techniques, including those techniques which utilize a small quantity of latex as a nucleating site for polymerization. Generally, seeding results in the polymerized latex being of greater average particle size.
In addition to the foregoing components, the composition of the invention may also contain various supplemental plasticizers. The principal purpose of such materials is to adjust the degree to which the cured films produced from the composition are plasticized. These are solvent-type plasticizers, i.e., rather high boiling, normally liquid organic compounds which are chemically inert toward the polymer, in which the copolymer is at least partially soluble and will therefore be readily softened by contact with the plasticizer. Appropriate plasticizers of this type include naphthenic and aromatic petroleum oils and synthetic organic compounds such as ester-type plasticizers and liquid polymers. Suitable ester-type plasticizers include the following: hexylene glycol, dimethyl phthalate, dibutyl phthalate, chlorinated diphenyls, tributyl phosphate, di-carbitol phthalate, dibutoxy-glycol phthalate, dimethoxy-glycol phthalate, butyl phthalyl butyl glycolate, methyl phthalyl ethyl glycolate, triglycol di-2-ethylbutyrate, tri-glycol di-2-ethylhexoate and phosphate-type plasticizers such as tributoxyethyl, tricreasyl, triphenyl, diphenyl octyl, diphenyl cresyl, tris-dichloropropyl, tris-chloroethyl, tris-dibromopropyl, and tris-dichloroisopropyl phosphates. Low molecular weight water-insoluble polyalkylene glycols, e.g. polypropylene glycols, are also suitable plasticizers. Also, liquid polymers may be used as plasticizers, for instance, liquid polybutylenes, liquid polybutadienes and liquid polyesters. Other materials such as antioxidants, defoamers, bactericides, emulsifiers, thickeners, dispersants and the like may be used in the present composition.
A wide variety of granular starches may be utilized in the present composition. For instance, granular starch derived from both root and cereal sources such as corn, potato, tapioca, wheat, waxy sorghum, waxy maize, grain sorghum, and rice. However, it is preferred that the granular starches used be modified by oxidation, acid treatment, ethoxylation and the like to lower the molecular weight of the starch but not to substantially destroy the granular structure of the starch and thus make it cold water soluble. It will be appreciated that mixtures of these starches may be used. The cold water solubility of the granular starch used in the present composition should be below about 30 percent by weight and preferably be below about 20 percent by weight. For purposes of the present invention, dextrins come within the definition of starch and may be used provided their cold water solubility characteristics fall within the above enumerated criteria.
Modification of granular starch by acid- and oxidative methods are well known in the art and there are presently commercially available a relatively large number of starches which have been modified by such methods.
The presence of granular starch will sometimes cause an increase in viscosity of the latex composition during storage. This change in viscosity can be avoided by having present in the composition a water-soluble polymeric thickening agent. Exemplary of such thickening agents are polyacrylates, hydrolyzed polyacrylonitriles and salts thereof and various alkyl ethers of cellulose, such as hydroxypropyl methyl cellulose, and hydroxyethyl methyl cellulose.
In order to more clearly describe the nature of the present invention, specific examples will hereafter be described. It should be understood, however, that this is done solely by way of example and is intended neither to delineate the scope of the invention nor limit the ambit of the appended claims.
In the Examples, various tests are referred to. These tests were performed by the following methods.